"The route I would take would involve a conventional suppressor on the front, with a sleeve that telescopes over the barrel that is the same diameter (1") as both the suppressor and the receiver. A little O-ring groove in the barrel so the sleeve will be sealed at the rear. You could then drill (I would EDM, but I'm not set up for that) holes in the barrel and they would expand into the chamber between the thinned barrel and the inside of the sleeve. Since your suppressor can be conventional, you get all of the advantages of superior suppression but the added benefit of the around-barrel bleed chamber.If I understand you right, this defeats your purpose of having a monolithic upper but so be it."

Their comment and this video I watched (at the 1:00 mark) a while ago:

got me to do a little thinking. Instead of trying to squeeze everything into a small 1" OD piece of tubing, why not just fit up the frame to a large diameter receiver?

This is a 1.25" OD piece of tubing that I had laying around.

It might cause me to have to make some changes to the mechanicals, but for the increased volume, I think it'll probably be worth it.